Certain cognitive disorders manifest as distorted perception of the physical world. For example, studies have indicated that patients with body dysmorphic disorder or obsessive-compulsive disorder are more likely to modify a digital image of their face to match their own expectation of what their face looks like. The proposed study aims to understand the neural basis for such expectation effects, based on a hypothesis of how expectation signals modify processing of physical stimuli. By combining a perceptual task where a cue biases the behavior with single-unit electrophysiology in primates, expectation effects on the neural representation of external stimuli will be sought. In particular, one possible mechanism for expectation- related behavioral changes predicts that an expectation signal increases neural sensitivity and improves the ability to predict behavioral performance from the neural response. These studies will help reveal how expectation-induced changes in sensory representation might underlie perceptual discrepancies in certain cognitive disorders.